ASoC: rt5677: fix rt5677 spi driver build

Create a separate module for rt5677 spi driver. Without
this patch, the build fails due to multiple defs of
'init_module' and 'cleanup_module'. module_spi_driver()
defines its own module, so it can't be part of the rt5677
module.

Signed-off-by: Ben Zhang <benzh@chromium.org>
Signed-off-by: Mark Brown <broonie@kernel.org>